Wi-Fi is a flexible, short-range data communications technology used to connect devices as diverse as notebooks, tablets, handsets, consumer electronics, smart utility meters and much more. Wi-Fi technology is widely used to provide wireless internet access in public places like airports, hotels and shopping centers, and is also used in the home and office to allow a wide range of devices to access the internet and network with each other without the need for special cables. Wi-Fi devices use low-power radio waves in the 2.4 and 5 GHz range to transmit and receive data over the air. Wherein the greater the Wi-Fi transmit power, the long the range of the Wi-Fi enabled device. However, Wi-Fi devices operate at frequencies that may be potentially harmful to humans when enough radio frequency (RF) power output is produced from the Wi-Fi device. The FCC and other federal governmental agencies around the world require that any wireless device be evaluated to meet RF exposure limits set forth in governmental regulations, e.g., Specific Absorption Rate (SAR) levels.
Therefore a SAR test is necessary in determining maximum allowable RF power output when the Wi-Fi enabled device is in close proximity to a user. The Specific Absorption Rate (SAR) is the unit of measurement for the amount of radio frequency (RF) absorbed by the body when using a wireless device. The SAR value is expressed in terms of watts per kilogram (W/kg) or milliwatts per gram (mW/g). The RF exposure limits used are expressed in the terms of SAR, which is a measure of the electric and magnetic field strength and power density for transmitters operating at frequencies from 300 kHz to 100 GHz. The most generally accepted method for measuring SAR values is the direct method SAR test. This method utilizes a model called a “SAM phantom” to simulate the human head and a “flat phantom” to simulate the human body. With this method, wireless devices are tested at the highest certified power level in laboratory conditions utilizing a SAR test system with a robot.
Therefore, with Wi-Fi enabled devices, it may not be safe for a user of the device if the Wi-Fi feature of the device is in operation at its maximum RF power output when in close proximity to the user's body. It also may not be safe for the Wi-Fi transmitter amplifier used in the device to operate when in close proximity to a large metal object, e.g., metal table top. Thus, Wi-Fi enabled devices need a reliable system, method and apparatus for detecting the presence of a user near the Wi-Fi antenna and the presence of large metal objects.